You mean old Pro4AAA. that looks like that phones chopper pilot has on his head, right?
As far as I heard, that phone was the top of the line at its time about 30 years ago. But I do not think its still on the same spot in these days. Things have been changed, so headphone world is.
About the Pro4AAT which is successor of Pro4AAA, which is supposed to sound identical or better than old Pro4AAA. It looks like people have two extremely different idea regarding that phone. Quite lot of people say "meh" just like eric did, and a few people say its "great".
For me, I have love and hate situation with that.
The phone requires quite lot of power, so headphone amp is a must to take out its full power. It takes quite long time to open up its sound. "great" when it comes to its bass department, the bass was the one of the tightest bass I ever heard, but its little "meh" for other departments. It feels little stuffy and congested due to its closed design and especially its weight is too heavy to be comfortable.